Compression Fitting Valve - With or Without Putty

I installed 4 shut-off valves under two sinks yesterday using compression fitting valves. Both sides (they are two by two under each sink) seem to have leaked one or two drops of water over night.

I followed the instructions carefully, cut the 1/2" copper pipe using a pipe cutter, sanded the pipes to a smooth surface, gently tightend the ring and nut WITHOUT USING PLUMBERS PUTTY.
Now, I've read that some online diy'ers recommend using putty with the compression fittings, while other DON'T.

I know I am not supposed to overtighten the nuts, which I didn't but after the first test, they leaked a bit, and I tightened quite hard and it helped, but as I said, still a drop or two of water.

Should I remove the nut and try again...? With or without putty?

Thanks for your input!!!

Depending on the brand, the threads may not be the greatest. A small drop of oil on the threads before assembling makes it much smoother when tightening it down. It can catch if the threads aren't clean and appear to be tighter than it really is. You may only need another 10-degrees, but if the threads aren't well done, sometimes it is hard. You shouldn't need anything on the threads to seal things....the threads don't seal it, the compression ring does. The nut compresses the ring around the pipe and into the body of the shutoff to make the seal. Give it a little more. Note, you need two wrenches...one to hold the body of the valve, and a second one to turn the nut. If you try it with only one, it's hard to get it sealed.

Jim is right.
At most, a drop of oil on the threads, and tighten some more.

I've never heard of putting putty on a pressure joint before.
That tip must be from an unhandy page.

valve

I always take the valve from the package and install it right onto the tubing. No "putty", joint compound, Teflon tape, or oil.

Thanks all!
I wish I knew about the "oil trick"....
I loosened the nuts a little bit, and tightended a bit more, and so far it seemed to work.

Yeah, not sure if plumbing is a science or art....science there is a definite solution, while art implies various interpretation.
Either way...I appreciate your professional advice and opinions.
So far it's fun, rewarding and educational!

Here is another option for the future.

Just buy a sweat on valve and solder it to the pipe I've never had a leak yet when I solder I can't say the same for compression fittings.

My rule is that I never use a compression fitting for any pipe over 3/8".